At the western edge of Mumbai, Versova Beach was once a rubbish and plastic graveyard. Today, after two years of volunteer efforts to clean it, hatchlings from a vulnerable turtle species have been sighted decades after they disappeared due to the acute pollution of this stretch of beach along the Atlantic Ocean.

“I had tears in my eyes when I saw them walking towards the ocean,” says lawyer and environmental activist Afroz Shah, who initiated what UN Environment calls the “world’s largest beach clean-up project”. Shah estimates that more than 12,000 tonnes of plastic have been removed from Versova Beach, thanks to the massive volunteer clean-up operation. About 55,000 people live in slums along the coastline of India’s largest city, and over 1,000 volunteers participated in the work.

Versova Beach is a local example of the global problem of plastic waste. Volunteer pickup projects are no solution to the millions of tonnes of plastic estimated to be accumulating in the ocean. Plastic has made its way into all marine ecosystems on Earth – from the open ocean surface in the South Pacific Gyre to the deepest part of the world’s ocean, the Mariana Trench. It can be found in even the most remote areas in the Arctic and Antarctic. Over the past few years, plastic pollution as a global problem has caught the eye of the public as well as of researchers and policymakers around the world.

Sea turtles have again been sighted at Versova Beach, after a massive clean-up innitiative that cleared the beach from more than 12,000 tonnes of plastic.

Plastic waste is a global problem, but what exactly is the problem? Negative effects, such as filling sea birds’ and turtles’ stomachs, are known, but researchers are concerned there may be more unknown effects looming on the horizon. Could plastic affect the way the Earth functions? If so, it could be considered within the framework of planetary boundaries – the safe operating space for humanity. Researchers from the Stockholm Resilience Centre at Stockholm University (publisher of Rethink) and GRID-Arendal (a Norwegian foundation working with the UN Environment Programme) have investigated whether plastic pollution could be considered a part of the planetary boundary for “chemical pollution and the release of novel entities”.

What’s the problem with plastic?

Bits of plastic have been found everywhere in the ocean. They can come from car tyres, packaging, cosmetics, hygiene products, and clothes. One of the major problems with plastic is that it doesn’t completely degrade – it just breaks down into smaller and smaller fragments when it is exposed to sunlight and ocean waves, or when consumed by animals.

Versova Beach before the clean-up. Photo: Afroz Shah

Marine wildlife choke on plastic bags and plastic straws. Researchers at Plymouth University say nearly 700 marine species are threatened by marine plastic pollution.11. S.C. Gall, R.C. Thompson, The impact of debris on marine life, Mar. Pollut. Bull. 92 (2015) 170–179 Link to articleSee all references
And it’s not just large plastic pieces that are a potential threat: microplastics – or plastic particles that are smaller than 5 mm – are impossible to remove with current technologies once they find their way into the environment. But even though the plastic pieces may be invisible to the human eye, they are still damaging ecosystems.

The harmful effects of plastic can come from substances added during plastic production, for example flame-retardants and dyes, as well as from other toxic chemicals that stick to and accumulate on plastic particles, entering the marine environment and food chain.22. UNEP (2016) Marine plastic debris and microplastics – Global lessons and research to inspire action and guide policy change. United Nations Environment Programme, Nairobi.Link to reportSee all references
Researchers have found that some species exposed to high concentrations of hormone-disrupting chemicals, such as Bisphenol A and phthalates used in plastic production, pass adverse reproductive effects onto their offspring generations later.33. Heindler, F. M., Alajmi, F., Huerlimann, R., Zeng, C., Newman, S. J., Vamvounis, G., & van Herwerden, L. (2017). Toxic effects of polyethylene terephthalate microparticles and Di (2-ethylhexyl) phthalate on the calanoid copepod, Parvocalanus crassirostris. Ecotoxicology and environmental safety, 141, 298-305.See all references
These chemicals have been found to interfere with the human hormone system, and may be related to increased risks of cancer, reproductive difficulties, behavioural disorders, and other human health problems.44. Vom Saal, F. S., Akingbemi, B. T., Belcher, S. M., Birnbaum, L. S., Crain, D. A., Eriksen, M., ... & Ho, S. M. (2007). Chapel Hill bisphenol A expert panel consensus statement: integration of mechanisms, effects in animals and potential to impact human health at current levels of exposure. Reproductive toxicology (Elmsford, NY), 24(2), 131.See all references

How microplastics affect human health remains largely unknown and needs more research. Because some of these toxic chemicals don’t break down, scientists suspect that they can stick to and accumulate on plastic particles that then enter the environment and eventually travel up the food chain, potentially reaching humans. Microplastics have found their way into an extraordinary range of products, such as honey and sugar, shellfish, cultured mussels and oysters, bottled water, and table salt.22. UNEP (2016) Marine plastic debris and microplastics – Global lessons and research to inspire action and guide policy change. United Nations Environment Programme, Nairobi.Link to reportSee all references

An ever-increasing number of studies report on the threats that plastic poses to the environment and to human health. Still, consumer habits, industry activities, and policies are only now beginning to change.

Where does all this plastic come from?

Global plastic production has risen from around 2 million tonnes a year in the 1950s to around 380 million tonnes in 2015. Estimates are that more than 8.3 billion tonnes have been produced since the early 1950s.55. Geyer, R., Jambeck, J. R., & Law, K. L. (2017). Production, use, and fate of all plastics ever made. Science advances, 3(7), e1700782. DOI: 10.1126/sciadv.1700782See all references
With the exception of materials that have been incinerated, approximately 80% of all the plastic that has ever been produced is still around, mainly in landfills or the natural environment.66. Jambeck, J. R., Geyer, R., Wilcox, C., Siegler, T. R., Perryman, M., Andrady, A., ... & Law, K. L. (2015). Plastic waste inputs from land into the ocean. Science, 347(6223), 768-771.See all references
Around 8 million tonnes of bulky plastic waste – and an additional 1.5 million tonnes of microplastics – enter the world’s ocean every year.77. Boucher, J., & Friot, D. (2017). Primary microplastics in the oceans: a global evaluation of sources. Gland, Switzerland: IUCN.See all references
Carried by waves and ocean currents, plastic also accumulates along shorelines of densely populated coastal communities.

If plastic production, recycling, and consumption behaviour don’t change drastically, an additional 33 billion tonnes of plastic waste will be dumped in landfills or the environment by 2050.88. Rochman, C. M., Browne, M. A., Halpern, B. S., Hentschel, B. T., Hoh, E., Karapanagioti, H. K., ... & Thompson, R. C. (2013). Policy: Classify plastic waste as hazardous. Nature, 494(7436), 169.See all references
Many of these plastic products, such as wrappers and other packaging materials, are disposables designed for a single use after which they are thrown away. Only around 9% of used plastic is recycled globally.55. Geyer, R., Jambeck, J. R., & Law, K. L. (2017). Production, use, and fate of all plastics ever made. Science advances, 3(7), e1700782. DOI: 10.1126/sciadv.1700782See all references

Many developed countries have chosen to export plastic waste to be recycled in developing nations. Meanwhile, developing countries are trying to tackle plastic waste but do not have the resources or recycling systems in place to deal with the scale of the problem. But things are starting to change. Now China, for example, has banned all imports of waste materials from other countries. This increases the pressure on waste-exporting countries to find more sustainable ways to dispose of and recycle waste.

The planetary impact of sea plastic

The mismanagement of plastic waste can increasingly be felt on a global scale. Researchers are now looking at the impact of plastic on the Earth system and the planetary boundaries. The planetary boundaries are the limits of natural systems or processes that keep Earth in a relatively stable state.99. Villarrubia-Gómez, P., Cornell, S. E., & Fabres, J. (2017). Marine plastic pollution as a planetary boundary threat–The drifting piece in the sustainability puzzle. Marine Policy.See all references
. Planetary boundary processes include climate change, ozone depletion, and ocean acidification.1010. Galloway, T. S., & Lewis, C. N. (2016). Marine microplastics spell big problems for future generations. Proceedings of the National Academy of Sciences, 113(9), 2331-2333.See all references
Could the concentration of plastic in the ocean, today or in the future, go beyond critical thresholds leading to global effects in these processes? Could plastic pollution be considered a key component of the planetary boundary associated with chemical pollutants?

These questions have been explored by researchers at the Stockholm Resilience Centre (SRC) and GRID-Arendal (GRID), who have evaluated existing knowledge of the effects of plastic pollution in marine ecosystems on a planetary scale – from large plastic items to microplastics and even smaller nanoplastics.99. Villarrubia-Gómez, P., Cornell, S. E., & Fabres, J. (2017). Marine plastic pollution as a planetary boundary threat–The drifting piece in the sustainability puzzle. Marine Policy.See all references
The research team looked at the direct and indirect effects of marine plastic pollution on marine wildlife, as well as changes across time, space, and ecosystems.

Chemical pollution experts have argued that pollutants posing a threat to the Earth system must meet three main conditions simultaneously in order to be regarded as part of the planetary boundary for chemical pollution and the release of novel entities. First, the pollution must be irreversible or very difficult to reverse; second, the disruptive effect must not be discovered until it is a problem at the global scale; and third, the pollution must disrupt Earth system processes.1111. MacLeod, M., Breitholtz, M., Cousins, I. T., Wit, C. A. D., Persson, L. M., Rudén, C., & McLachlan, M. S. (2014). Identifying chemicals that are planetary boundary threats. Environmental science & technology, 48(19), 11057-11063.See all references

For the first condition, the SRC and GRID research team found evidence that suggests marine plastic pollution is indeed irreversible. Plastics are everywhere in the environment. They are even considered to be a geological marker of the Anthropocene,1212. Zalasiewicz, J., Waters, C. N., do Sul, J. A. I., Corcoran, P. L., Barnosky, A. D., Cearreta, A., ... & McNeill, J. R. (2016). The geological cycle of plastics and their use as a stratigraphic indicator of the Anthropocene. Anthropocene, 13, 4-17.See all references
or the Age of Humans: plastic is a new type of material that will be encapsulated in rocks all over the planet, for future geologists to study as a marker of the current geological time period, in which human activity has become the dominant influence on the environment.

From microscopic to global scale, marine plastic pollution could be affecting important Earth system processes

The second condition – where the disruptive effects of a pollutant might not be discovered before they become a problem at a planetary scale – is less clear-cut, but since plastic is being redistributed across land and around the world’s ocean, the concentrations of it as a contaminant are nearly the same globally. This means crossing critical thresholds would happen in very many places at once, so plastic also meets the second condition.

The second condition also encompasses other scenarios that the chemical pollution experts at Stockholm University have suggested, which fit other ways in which plastic may be affecting natural systems worldwide – depending on how “planetary scale” is defined. On some beaches microplastics are present in such high concentrations in the sediment that they may be changing the flows of nutrients and water. Plastic on heavily polluted beaches also affects the sand’s surface temperature, which can affect sex determination in sea turtles’ eggs – an already endangered species and a key species in marine ecosystems.1313. C.L. Yntema, N. Mrosovsky, Critical periods and pivotal temperatures for sexual differentiation in loggerhead sea turtles, Can. J. Zool. 60 (1982) 1012–1016.See all references
These are local effects, but may happen in several places across the globe – one scenario.

Research also shows that copepods –­ tiny crustaceans that play a crucial role in marine food webs – produce fewer and less-healthy offspring if they consume large amounts of microplastics.1010. Galloway, T. S., & Lewis, C. N. (2016). Marine microplastics spell big problems for future generations. Proceedings of the National Academy of Sciences, 113(9), 2331-2333.See all references
Such changes could lead to booms or collapses of important species that eat copepods, with knock-on effects over time in entire ecosystems and the Earth system processes they maintain – another scenario. The time delay between exposure to plastic and possible effects – the fourth scenario – helps to explain why there is still so much scientific uncertainty about the extent to which marine ecosystems are affected by plastic pollution.

For the third main condition, the disruption of Earth system processes, the researchers looked at how carbon is captured and stored in the ocean. The tiny copepods that play such a vital role in food webs also influence the flow of carbon in the ocean and its eventual burial and storage in ocean sediments. Scientists have found that if copepods have eaten microplastics, their faeces doesn’t sink down into the water as fast as usual. That change in settling rate also changes the flow of carbon and nutrients in the ocean.1414. M. Cole, P. Lindeque, E. Fileman, C. Halsband, T.S. Galloway, The impact of polystyrene microplastics on feeding, function and fecundity in the marine copepod
Calanus helgolandicus, Environ. Sci. Technol. 49 (2015) 1130–1137, Link to articleSee all references
The consequences are still unknown but may be linked to climate change – which means that microplastics could affect one of the biggest Earth system processes and planetary boundaries.

Other recent research is providing more evidence of links between marine plastic pollution and climate change. For example, sunlight accelerates the breakdown of plastic, which releases methane – a powerful greenhouse gas.1515. Royer S-J, FerroÂn S, Wilson ST, Karl DM
(2018) Production of methane and ethylene from
plastic in the environment. PLoS ONE 13(8):
e0200574.Link to articleSee all references
Another climate kick could come from microplastics floating on the surface of Arctic waters: here they might interfere with the formation and melting of the ice cover, which could lead to climate change because polar ice reflects sunlight and slows warming.

From microscopic to global scale, marine plastic pollution could be affecting important Earth system processes.

Microplastics. Photo: Oregon State University/Flickr

Moving forward

Marine plastic pollution meets two of the three main conditions for it to be considered a chemical pollutant in the planetary boundary framework: it is irreversible and globally pervasive. But, “irrespective of whether marine plastic is integrated into the planetary boundaries framework, it is evident that marine plastic pollution is already implicated in global processes to a point that deserves much more careful monitoring and precautionary management”, says Sarah Cornell, an SRC researcher.

Many questions remain as to how marine plastic pollution affects the environment, but it is undoubtedly a global problem requiring immediate international attention. With millions of tonnes of plastic entering the seas every year, a globally coordinated approach is needed to tackle the vast and growing scale of plastic waste. International organisations, such as the UN, and countries with robust implementation of waste-management systems, such as Norway and Sweden, are working to create platforms for knowledge- and experience-sharing and providing funding to implement initiatives in countries where plastic pollution has become uncontrollable.

Research is needed to fill the many big gaps in understanding the effects of plastic pollution on ecosystems and people’s health. Education and innovation – along with strong commitment at local, national, and international levels – are needed to reduce plastic pollution and restore the health of coastlines and beaches.

The good news for this global environmental problem is that everyone can be part of the solution by simply using less plastic every day.